There has been proposed an exposure method which uses a photosensitive media sheet having a pressure-sensitive property, an image receiving sheet, and forms picture images on the image receiving sheet, as disclosed in the Japanese Patent Publication (Unexamined) No. 88739/1983. Further, the Japanese Patent Publication (Unexamined) No. 30537/1984 discloses a media sheet corresponding to all kinds of colors, in which the film is coated with three kinds of micro-capsules. The three kinds of micro-capsules are: (1) a Y micro-capsule containing a photo-curable ingredient sensitive to light within a blue wavelength range, and a colorless dye capable of coloring to yellow, (2) an M micro-capsules containing a photo-curable ingredient sensitive to light within a green wavelength range, and a colorless dye capable of coloring to magenta, and (3) a C micro-capsule containing a photo-curable ingredient sensitive to light within a red wavelength range, and a colorless dye capable of coloring to cyan.
Each of these micro-capsules is cured by exposing the micro-capsules to light within its sensitive wavelength range. After the exposure, the media sheet and an image receiving sheet are overlapped at their active surfaces under pressure, and hence, the uncured micro-capsules are crushed to reproduce picture images colored in all kinds of colors on the image receiving sheet.
There are two methods for exposing a media sheet corresponding to all kinds of colors to form latent images. One is to simultaneously expose the media sheet to light within a wavelength range of approximately 400 to 700 nm which includes blue, green, and red wavelength ranges. The other is to successively expose the media sheet to light within a wavelength range of approximately 400 to 500 nm which corresponds to a blue wavelength range, to light within a wavelength range of approximately 500 to 600 nm which corresponds to a green wavelength, and to light within a wavelength range of approximately 600 to 700 nm which corresponds to a red wavelength range, in accordance with the respective sensitivities of the Y, M, and C microcapsules.
In the successive exposure method, several pieces of digital picture image information, which correspond to yellow, magenta, and cyan, are previously written on three liquid crystals respectively. The media sheet is exposed only to light within the blue wavelength range separated from the light transmitted through the liquid crystal to which the yellow picture image information has been written, next, to light separated from the light transmitted through the liquid crystal to which the magenta picture image information has been written, and to light separated from the light transmitted through the liquid crystal to which the cyan picture image information has been written. Through these exposure, the Y, M, and C micro-capsules are cured to form latent images according to the digitized picture image information of all kinds of colors.
It is to be noted that this three-stepped exposure method has a drawback which results in deterioration in the color densities of three primary colors of yellow, magenta, and cyan. In addition, there is a severe difference in the characteristic curve between the reproduced color of each primary color and the reproduced color of a neutral grey. For these drawbacks, the conventional digital picture image processing technique can not reproduce color accurately, and requires a complicated light source controlling to obtain an accurate reproduced color.